Total and Free Carnitine
Does this test have other names?
Quantitative plasma carnitine, plasma carnitine, plasma acylcarnitine analysis
What is this test?
This test measures the amount of a substance called carnitine in your blood. It compares the amount of usable or "free" carnitine with the total amount in your body.
Carnitine is a compound that's present in nearly every part of your body. Your cells normally use the fats in your body for energy. Without carnitine, your body has trouble digesting fatty acids. It can't turn fats into energy and uses the sugar in your blood for energy instead.
Some people have a carnitine deficiency. If your body can't use carnitine, you have low blood sugar and can become weak, tired, and anemic. You may develop heart and kidney problems. Some people even develop progressive muscle diseases like muscular dystrophy.
Because about one in every 100,000 babies has a carnitine problem, newborns are usually screened for a condition called primary carnitine deficiency. Some people also develop a carnitine deficiency as a result of type 2 diabetes, cancer, heart problems, or kidney problems.
Getting tested helps your doctor determine whether you are able to use carnitine effectively.
Why do I need this test?
Your doctor may order this test if you are being treated for type 2 diabetes, cancer, an enlarged heart, or kidney disease. In some cases, these conditions can affect your ability to use carnitine.
This test is often given to babies shortly after birth or to toddlers, especially if they show signs of carnitine deficiency, such as eating problems, vomiting, confusion, seizures, and muscle weakness.
What other tests might I have along with this test?
If your doctor suspects you have another disease or inherited disorder, you may need other tests, including:
Complete blood count, or CBC, to screen for blood disorders, such as anemia
Serum electrolytes to screen for an imbalance of sodium, potassium, or other electrolytes in your blood
Blood glucose to measure your blood sugar and help diagnose diabetes
Tests to look for liver injury and disease
Blood gas to detect an acid-base imbalance in your blood
Urine tests to check your urine for signs of a kidney infection, urinary tract damage or infection, or diabetes
Your doctor may also talk to you about genetic testing if he or she suspects there is a genetic reason you can't absorb carnitine.
What do my test results mean?
Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.
Test results are a percentage of the amount of free carnitine compared with the total amount of carnitine in your blood. A ratio greater than 0.4 suggests you have a carnitine deficiency. Similarly, if your total serum carnitine is less than 40 micromoles per liter (μmol/L), you may have a carnitine deficiency.
Results also depend on your physical condition and age.
How is this test done?
The test requires a blood sample, which is drawn through a needle from a vein in your arm.
Does this test pose any risks?
Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.
What might affect my test results?
What you eat may affect the results of this test.
How do I get ready for this test?
Ask your doctor whether you should not eat or drink anything but water before this test. Also be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.
- Bass, Pat F. III, MD, MPH
- Stump-Sutliff, Kim, RN, MSN, AOCNS